


rules for sleeping with my brother/best friend

by spiritscript



Category: Haikyuu!!
Genre: Alternate Universe - College/University, Crack, Didn't Know They Were Dating, Friends With Benefits, Getting Together, Idiots, M/M, Osamu POV, POV Outsider, Sexual Content
Language: English
Status: Completed
Published: 2020-10-25
Updated: 2020-10-25
Packaged: 2021-03-08 17:08:45
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 1,895
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/27190186
Author URL: https://archiveofourown.org/users/spiritscript/pseuds/spiritscript
Summary: Rule Number One: I don't want to hear itThis rule means two things:1. I do not want to hear it happening.2. And I do not want to hear anything about it. Anything.How do you deal when your brother and best friend start sleeping together and maybe dating? Osamu's asking for his own sanity
Relationships: Miya Atsumu/Suna Rintarou
Comments: 30
Kudos: 266





	rules for sleeping with my brother/best friend

**Author's Note:**

> yeah I wrote this last night pretty much in one sitting between the hours of 12 and 1 am and between a completely self indulgent introspective piece and three very angsty pieces
> 
> What is this you ask. I have no idea but like, enjoy?

Osamu found out completely by accident. Which kind of felt right since it happened completely by accident. Not that Osamu knew this when he found out because after he walked into the kitchen, home early from work due to a power cut, to see them in the kitchen flirting (which they always did jokingly but it felt different this time) while Atsumu attempted to cook what Osamu assumed was breakfast with Rintarou wearing only his underwear and one of Atsumu’s t-shirts, Osamu promptly, swiftly, quickly left. 

How did Osamu put it together so quickly? There were three main tells.

> **1\. Rintarou wasn't on the couch when Osamu was leaving the house at half five for his shift that started in the coffee shop at six a.m.**
> 
> This one might be a bit of a stretch, but Rintarou, whenever he stayed over unexpectedly after a night of drinking, always slept on the couch. And it was only ten a.m. when Osamu got home, so there was no chance that after a night of heavy drinking, Rintarou had managed to crawl out of his hangover hole (because Rintarou gets the absolute worst hangovers) and just popped by for breakfast. Especially if it was Atsumu cooking.

> **2\. The t-shirt he was wearing was one of Atsumu’s favourites.**
> 
> Again, not solid evidence. But Asumu never let anyone wear it and the one time Osamu borrowed it at the age of sixteen, he took a pair of scissors to his favourite jeans. Maybe he had grown up, but also this was Atsumu and growing up had not been in his capabilities thus far.

> **3\. The large purple and blue mark on Rintarous neck coupled with matching one on Atsumu’s shoulder.**
> 
> This one speaks for itself especially when you consider it alongside the other two pieces of evidence.

“Samu!” his brother called down the hall after he’d left promptly, swiftly, quickly. “Samu!”

He stopped and turned to see his brother bare chested and plodding down the hall after him, another purple bruise visible on his chest.

“It’s not what it looks like. Well no, it is but -”

“Nope,” Osamu started walking again and Atsumu caught his arm and began to drag him back to the apartment. Osamu grumpily allowed himself to be dragged, but not easily. When he entered, Atsumu dragged him to the living room where Rintarou was standing watching the door, and dropped onto the couch behind him.

“Why on earth would you sleep with him?” Osamu asked incredulous, and Atsumu shot him a look.

“I don't know Samu,” he replied, his head falling back onto the couch, “I'm asking myself that too.” 

“I'm right here y’know,” Atsumu mumbled.

“Oh yeah right,” Osamu said and turned to face his brother, “so why the fuck did you sleep with my best friend? My best friend! Aren't there enough people out there that have nothing to do with me willing to sit on your dick or have you sit on theirs huh?”

“So crude Samu,” he tried to laugh weakly, but the look in Osamu’s eyes dried that up real quick. “It was an accident.”

Osamu’s eyes flashed and he bared his teeth ready to retort but Atsumu quickly began stuttering.

“No... no, no I know, no one slipped and fell on a dick, but it just... it just happened.”

Osamu furrowed his brows and pursed his lips.

“I dunno, we just, we did some shots -”

“Rintarou!” Osamu interjected, turning to look at his friend who began to curl in on himself, looking for all his life like he wanted to become part of the couch, “why did you do shots? Bad things happen when you do shots," he pointed at his brother.

“Hey, hey we are not here to slander my character!” Atsumu raised his hands in defense.

“We’re always here to slander your character.”

Osamu turned back to point at Rintarou now. "Don't you dare think you’re gonna win any points with me just by being a dick to ‘Sumu again."

Rintarou grinned and uttered the words that might as well be carved on Osamu’s grave stone as his cause of death because as soon as they were out of Rintarou’s mouth, his soul was out of his body. “Are we talking about my dick? Because he seemed to enjoy it last night.”

“That’s it,” Osamu said, the whiplash subsiding and the bile settling in his stomach again,“we’re making rules.”

And thus, the five rules were created.

**1.**

> **Rule Number One: I don't want to hear it**
> 
> This rule means two things: 
> 
> 1\. I do not want to hear it happening. 
> 
> 2\. And I do not want to hear anything about it. Anything.

_“It probably won’t happen again anyway,” Rintarou stated, as they sat around the coffee table, watching Osamu write the first rule in one of his notebooks and underline it._

_“Then call it precautionary,” he replied around the pen cap in his mouth._

It did happen again, and the first part of this first rule was the first to be broken. Osamu banged on the wall between their rooms and begged them to shut up. They did. 

Until it happened again. 

And again. 

Eventually they bought him earplugs in compensation and noise cancelling headphones for his birthday. They thought they were funny.

**2.**

> **Rule Number Two: No fucking anywhere in the apartment but ‘Sumu’s bedroom.**
> 
> If I find out you’ve done it on the couch where I sit, the shower where I wash, the floor where I lay down during my existential crises; you will regret it. And if I hear you've done it on the table or the kitchen counter or anywhere in the kitchen for that matter, I will show you, up close and personal, all the things I've learned to do with a knife.

_“Well obviously,” Atsumu said, “that doesn’t need to be a rule.”_

_Osamu shot him a look and he didn’t reply._

It took two months for this rule to be broken (or at least for Osamu to find out it had been broken). He had come home late from the library one night to find them in a serious state of compromise on the couch. The very first place he had written in the rules (now typed, printed, laminated and hung on the kitchen fridge) where they were not supposed to.

“We weren’t having sex though!”

“Oral sex is a type of sex!”

And then he walked in on them in the shower.

“But it’s self cleaning!”

“I don’t care!”

He hadn’t caught them in the kitchen and somehow he thinks he never will because they probably don’t want to find out just how serious he had been about the knives.

**3.**

> **Rule Number Three: I’m not a couples counselor and so should not be asked for advice in any capacity.**
> 
> This relates back to point one - I don’t want to hear about it.

_“As if I would come to you for advice anyway,” Atsumu snorted._

Of course he did. Atsumu is, if anything, a disaster of a human and so when the day before Rintarou’s birthday arrived about six months into their ‘arrangement,’ (we’re not dating, they insisted and yet they still fell into each other’s beds every other night even when they weren’t drunk) Atsumu was knocking on Osamu’s door, face twisted into something horrible and nothing like he ever wanted to see - he was worried.

“What the hell do I get him?”

Funnily enough, he had seen pretty much the same scene three months before that outside of his apartment door the day before Atsumu’s birthday because his best friend is also a complete disaster. 

“I don’t know what to get him.” Rintarou had whined and walked to the kitchen cupboard, helping himself to some cookies.

“I hope you remember it’s also my birthday tomorrow.” 

“Yeah, we already got you something,” he grinned wickedly. (It was the noise cancelling headphones and as much as Osamu hated the reasoning, they were really good headphones)

So he found himself breaking the very rules he created.

**4**

> **Rule Number Four: No PDA**  
>  I do not want to become a third wheel. 

_“We’re not dating, it’s probably not going to happen again, this is unnecessary.” Rintarou mumbled, the hangover really starting to hit him as he curled up on the couch._

_“What he said.” Atsumu mumbled, his head on Osamu’s shoulder._

__

_He ignored both of them._

It was over a year before this rule was broken, (because they ‘weren’t dating’ just spending a lot of time together without Osamu - which wasn’t frequent before they began sleeping together, and sleeping together a lot, sometimes not even having sex - so PDA didn’t happen because they had no reason to show off that they were together or something like that. The language of emotionally stunted idiots is not something he is fluent in) and it was broken disastrously. 

The three of them were on a night out and Osamu felt himself being turned around forcefully, almost spilling his drink.

“Who the hell is that and what are they doing?” Atsumu asked, pointing to where Rintarou was laughing with someone.

“‘Sumu -”

“Oh right, ‘you don’t want to hear about it, you aren’t a relationship counsellor, this is none of your concern,’” Atsumu bit out, not even looking at him, his brow furrowed and teeth gritted. 

That was not what Osamu was going to say because really those rules had been abandoned a long time ago. What he was going to say was that the person Rintarou was talking to was a friend from uni who was very much in a relationship and Atsumu didn’t have anything to worry about. But, of course, his brother is a disaster and an idiot so he never had the chance.

“I’ll deal with this myself,” Atsumu said and walked over to them. Osamu watched as he slipped a hand in Rintarou’s pocket then slid it up and around his waist. He stood beside him, and pulled Rintarou into him, fixing the other boy with a glare (squaring up to him would probably be a better description). Rintarou turned to look at him and Atsumu planted a big, fat, horrible kiss on his forehead.

Then they fought about jealousy or idiocy or rudeness or something and Osamu had to be the one to drag them home, sit them down, and slap them across the back of their thick skulls.

“Just admit you’re dating already and sort this shit out because you both obviously like each other and for some fucking reason, you two actually work really well together.”

They tried to keep the PDA to a minimum after that, but now that they knew where they stood with each other, they seemed to find it a lot harder.

**5.**

> **Rule Number Five: Do not hurt my brother/best friend or I will have to hurt you.**
> 
> I’m serious. 

_“Aww ‘Samu, ya getting all protective of your brother?” Atsumu lifted his head and reached to pinch his cheek, but he moved backwards and out of the way to avoid it. Unfortunately Rintarou had been waiting._

_“Awk, you being all cute and protective of us?” He did manage to pinch Osamu’s cheek._

_“Fuck off both of you,” he replied and stood up. “Just follow the rules and use condoms.”_

This is the only rule that has yet to be broken.

**Author's Note:**

> I can also be found on [twitter](https://twitter.com/ohmiyamy/status/1320411759111524356?s=20)!


End file.
